Snake River dams lose lots of water to evaporation, study says

By Jennifer Yachnin | 01/16/2025 01:39 PM EST

An advocate noted a Stockholm Environment Institute study found the annual evaporation of water kept in reservoirs is 17 percent of the water currently used for agricultural irrigation.

An Army Corps of Engineers official looks over the 10 spillways at Ice Harbor Lock and Dam on the lower Snake River.

An Army Corps of Engineers official looks over the 10 spillways at Ice Harbor Lock and Dam on the lower Snake River on June 6, 2005, near Burbank, Washington. Jeff T. Green/AFP via Getty Images

Breaching four hydropower dams and draining their respective reservoirs on the Lower Snake River could boost water supplies currently lost to evaporation enough to support 240,000 people, according to a newly published study.

The nonprofit Stockholm Environment Institute issued the analysis Thursday on evaporative losses on the Pacific Northwest waterway. The organization received support for the project from Columbia Riverkeeper, the Water Foundation and Patagonia, all of which have endorsed removing the dams in a bid to support struggling salmon and steelhead populations.

The report found that across the four reservoirs created by the Ice Harbor, Lower Monumental, Little Goose and Lower Granite dams, about 30,400 acre-feet of water is lost each year to evaporation.

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An acre-foot of water is equal to about 326,000 gallons, or enough water to support two to three average families annually. The amount of water lost to evaporation on the Lower Snake River — about 9.9 billion gallons — could also flush nearly 6.2 billion toilets at the federal standard of 1.6 gallons per flush.

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